The present invention relates to a method for removing a halogen series gas comprising a halogen element or a halogen compound. It relates to a method for removing a halogen series gas from e.g. dry etching exhaust gas containing a halogen series gas for example.
Conventionally, as a method of treating e.g. dry etching exhaust gas or an exhaust gas from a CVD (chemical vapor deposition) chamber containing a halogen series gas comprising a halogen element or a halogen compound, a treatment method by dry process employing an adsorbent such as activated carbon has been employed in order to miniaturize equipments and to simplify operation. However, there are drawbacks such as firing due to heat of adsorption during gas adsorption, odor of a used adsorbent and making a solid waste residue.
In consideration of these circumstances, it is an object of the present invention to provide a method for removing a halogen series gas, which suppresses firing of an adsorbent, which has a high performance of treating a halogen series gas, and which reduces odor of a used adsorbent and making a solid waste residue.
The present invention provides a method for removing a halogen series gas, which comprises bringing a halogen series gas comprising a halogen element or a halogen compound into contact with a granulated product, wherein the granulated product is obtained by granulating a powder of a hydrogencarbonate having a mean particle diameter of primary particles of from 10 to 500 xcexcm, and has a mean particle diameter of from 0.5 to 20 mm and an average hardness as defined below:
in a case where the granulated product has a mean particle diameter of at least 0.5 mm and less than 1.0 mm, the average hardness of granulated product particles having particle diameters of at least 0.5 mm and less than 1.0 mm is at least 1 N;
in a case where the granulated product has a mean particle diameter of at least 1.0 mm and less than 1.5 mm, the average hardness of granulated product particles having particle diameters of at least 1.0 mm and less than 1.5 mm is at least 4 N;
in a case where the granulated product has a mean particle diameter of at least 1.5 mm and less than 2.0 mm, the average hardness of granulated product particles having particle diameters of at least 1.5 mm and less than 2.0 mm is at least 10 N; and
in a case where the granulated product has a mean particle diameter of from 2.0 mm to 20 mm, the average hardness of granulated product particles having particle diameters of at least 2.0 mm is at least 30 N.
Now, the present invention will be described in detail with reference to the preferred embodiments.
In the present invention, as the hydrogencarbonate, sodium hydrogencarbonate or potassium hydrogencarbonate may, for example, be used. Particularly preferred is sodium hydrogencarbonate since it can be available in large quantities at a low cost and it is thereby suitable for industrial use, and it has no hygroscopicity, such being convenience for production and preservation of a granulated product. On the other hand, potassium hydrogencarbonate is preferred in a case where inclusion of sodium in e.g. an exhaust gas after the removal treatment has to be prevented.
In the present invention, a powder of the hydrogencarbonate is formed into a granulated product. The granulated product preferably contains the hydrogencarbonate in an amount of at least 70 mass %. If the hydrogencarbonate is less than 70 mass % in the granulated product, a gas removal capacity as a halogen series gas removing agent tends to decrease, whereby a removing agent packed bed has to be renewed frequently. The content of the hydrogencarbonate is particularly preferably at least 80 mass %. Here, as another material which may be contained in the granulated product, an adsorbent other than a hydrogencarbonate or a binder may, for example, be mentioned.
In the present invention, as the powder of a hydrogencarbonate, one having a mean particle diameter of primary particles of from 10 to 500 xcexcm is used, in view of easiness in granulation and availability in an industrial scale. If the mean particle diameter of primary particles is less than 10 xcexcm, flowability tends to be poor and operation such as particle handling tends to be difficult. If it exceeds 500 xcexcm, production of such a granulated product tends to be technically difficult, thus causing increase in cost. Here, primary particles are single crystals of a hydrogencarbonate, and the mean particle diameter is a mean particle diameter on the basis of mass.
In the present invention, the mean particle diameter of the granulated product of the powder of a hydrogencarbonate is from 0.5 to 20 mm. When the mean particle diameter of the granulated product is from 0.5 to 20 mm, a conventionally used packed tower or the like can be used during treatment of a halogen series gas. If the mean particle diameter of the granulated product is less than 0.5 mm, pressure drop tends to be high when a halogen series gas or a gas to be treated containing it passes through e.g. a packed bed. If the mean particle diameter exceeds 20 mm, the contact area of the granulated product with the gas to be treated tends to decrease, thus decreasing an exhaust gas removal performance. The mean particle diameter of the granulated product is particularly preferably from 0.5 to 10 mm.
In the present invention, the mean particle diameter of the granulated product is measured as follows. Sieves having sieve openings within ranges fit for the particle diameters of the granulated product are overlaid on top of one another, a bottom tray is disposed at the basement, and the granulated product is sprinkled on the top sieve, followed by shaking by a Ro-Tap Sieve Shaker. Then, a mass of oversize particles remaining on each standard sieve is measured, a cumulative mass of the oversize particles on each of the sieves having the respective sieve opening values is shown by a line graph, and the particle diameter when the cumulative mass of the oversize particles is 50% is taken as the mean particle diameter. As the difference in the sieve opening between adjacent sieves, a pitch of 0.5 mm is preferably employed, although it depends on the particle diameters of the granulated product.
In the present invention, the granulated product can be obtained by various methods such as compression molding, extrusion molding, rotating granulation and agitation granulation. Here, compression molding is particularly preferred since steps are simple and can be carried out industrially easily, and the granulated product can be obtained without using a binder, and further, a granulated product having a high hardness and is less likely to break, which has a large gas treatment capacity, can be obtained.
As a method to obtain the granulated product, a method of carrying out molding by dry process by using a compression molding machine, followed by coarse crushing and sieving may, for example, be mentioned. Further, a method of carrying out molding by a wet type granulating machine by using a water-soluble binder, followed by drying, may also be mentioned.
In the present invention, in a case where the granulated product of the powder of a hydrogencarbonate is packed in a packed bed to treat a halogen series gas, if the strength is low, the granulated product tends to be powdered and the pressure drop tends to increase when the halogen series gas is passed through the packed bed in some cases. Accordingly, the strength of the granulated product is made high.
As a method of evaluating the strength of the granulated product in the present invention, hardness may be mentioned. Here, the hardness is a force which is required to break one particle of the granulated product by vertically applying a load from above for compression.
The method of evaluating hardness in the present invention is carried out with respect to a group of particles having uniform particle diameters, obtained by classifying particles of the granulated product depending upon the mean particle diameter. For example, with respect to the granulated product having a mean particle diameter of at least 1.5 mm and less than 2.0 mm, a sieve having a sieve opening of 1.5 mm and a sieve having a sieve opening of 2.0 mm are used for sieving to collect twenty particles which are on the sieve having a sieve opening of 1.5 mm and below the sieve having a sieve opening of 2.0 mm, and hardness of each particle is measured to take the average value thereof as a central value (hereinafter referred to as an average hardness) for the particle strength.
As a preferred hardness of the granulated product of the powder of a hydrogencarbonate in the present invention, in a case where the granulated product has a mean particle diameter of at least 0.5 mm and less than 1.0 mm, the average hardness of granulated product particles having particle diameters of at least 0.5 mm and less than 1.0 mm is at least 1 N; in a case where the granulated product has a mean particle diameter of at least 1.0 mm and less than 1.5 mm, the average hardness of granulated product particles having particle diameters of at least 1.0 mm and less than 1.5 mm is at least 4 N; in a case where the granulated product has a mean particle diameter of at least 1.5 mm and less than 2.0 mm, the average hardness of granulated product particles having particle diameters of at least 1.5 mm and less than 2.0 mm is at least 10 N; and in a case where the granulated product has a mean particle diameter of from 2.0 mm to 20 mm, the average hardness of granulated product particles having particle diameters of at least 2.0 mm is at least 30 N.
In the present invention, a halogen series gas comprising a halogen element or a halogen compound (hereinafter referred to as the present halogen series gas) is removed. For example, e.g. a dry etching exhaust gas containing the present halogen series gas is treated to remove the halogen series gas in said exhaust gas. As the halogen, fluorine, chlorine, bromine or iodine may, for example, be mentioned. Specifically, as the present halogen series gas, one member or at least two members selected from the group consisting of BCl3, CCl4, Cl2, Br2, I2, SiCl4, HCl, COCl2, F2, SiF4, HF, COF2, NF3, WF6, ClF3 and HBr may be mentioned.
In the present invention, the temperature of the present halogen series gas is preferably at least 40xc2x0 C. and less than 80xc2x0 C., whereby reactivity of the granulated product can be increased, the removal treatment can be carried out efficiency, and the effect of the granulated product will last for a long period of time. The temperature of the present halogen series gas itself may be made at least 40xc2x0 C. and less than 80xc2x0 C., or the temperature of e.g. a packed tower in which the granulated product is packed may be set to at least 40xc2x0 C. and less than 80xc2x0 C. If the temperature of the present halogen series gas is less than 40xc2x0 C., the reaction rate tends to decrease. Further, if it exceeds 80xc2x0 C., equipments such as a packed bed have to be made of an expensive heat resistant material or have to have a heat resistant structure, and operation tends to be difficult. The temperature of the present halogen series gas is particularly preferably at least 50xc2x0 C. and less than 70xc2x0 C.
In the present invention, the hydrogencarbonate reacts with a halogen element or a halogen compound to form a water-soluble salt. Since the hydrogencarbonate itself is water soluble, the granulated product after used for removal of the halogen series gas in an exhaust gas can be dissolved in water. Further, as mentioned hereinafter, a solid waste product can be decreased in a case where activated carbon is used together with the hydrogencarbonate, for example.
Since the hydrogencarbonate reacts with a halogen element or a halogen compound in the present halogen series gas to form a water-soluble salt, no odor may be generated, which is caused by desorption of a halogen element or a halogen compound as in a case of adsorption by activated carbon, and accordingly renewal operation of e.g. a packed bed can be carried out easily. Further, the hydrogencarbonate itself has fire-extinguishing properties, whereby there is no danger of firing.
In the present invention, it is also preferred to pack the granulated product in a column such as a packed tower together with activated carbon and to bring the present halogen series gas into contact therewith to remove the present halogen series gas. By such a method, not only removal amount of the halogen element or halogen compound can be increased, but also generation of odor from activated carbon can be decreased, as compared with a case where activated carbon alone is used. Specifically, a method of disposing the hydrogencarbonate and activated carbon in a layer structure in a column such as a packed tower may, for example, be mentioned.
Specific Halogen Series Gas
In a case where the present halogen series gas is a halogen series gas containing at least one member selected from the group consisting of Cl2, Br2 and I2 (hereinafter referred to as specific halogen series gas), the following three methods for removing the specific halogen series gas may be mentioned.
The specific halogen series gas may contain, in addition to a halogen element containing at least one member selected from the group consisting of Cl2, Br2 and I2, at least one halogen compound selected from the group consisting of BCl3, CCl4, SiCl4, HCl, COCl2, SiF4, HF, COF2, F2, NF3, WF6, ClF3 and HBr, and it may contain, in addition to a halogen element and a halogen compound, another gas, and it may contain e.g. an inert gas (such as argon gas or N2 gas), O2 gas, air, CO2 gas or H2O gas.
(1) Addition of Acid Gas
To the specific halogen series gas, at least one acid gas selected from the group consisting of hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide (hereinafter referred to as specific acid gas) may be added and brought into contact with the granulated product of a hydrogencarbonate, whereby reactivity of the hydrogencarbonate can be further improved, and the effect can be made to last for a longer period of time.
The addition amount of the specific acid gas is preferably from 1 to 100 vol % based on the total amount of the specific halogen gas under the same pressure at the same temperature. If the addition amount is less than 1 vol %, no adequate effect of addition of the specific acid gas can be obtained. Further, if the addition amount exceeds 100 vol %, no further improvement in reactivity of the hydrogencarbonate can be confirmed, and an unnecessary amount of the specific acid gas may be used, and further, the hydrogencarbonate is consumed by reaction with the specific acid gas, and the capacity to remove the present halogen gas tends to decrease. A more preferred addition amount is from 1 to 80 vol %.
Here, as a method of adding the specific acid gas to the specific halogen series gas to bring the specific acid gas into contact with the granulated product of a hydrogencarbonate, the specific acid gas may be preliminarily added to the specific halogen series gas, followed by mixing, and then the mixture may be brought into contact with the hydrogencarbonate, or the specific acid gas may be brought into contact with the hydrogencarbonate when the specific halogen series gas is brought into contact with the hydrogencarbonate. Otherwise, in a case where the boiling point of the specific halogen series gas or the specific acid gas is high, they are brought into contact with the hydrogencarbonate preferably in a gas state by raising the temperature during contact or by diluting them with another gas.
Addition of the specific acid gas to the specific halogen series gas improves reactivity of the hydrogencarbonate with the specific halogen series gas, and a larger amount of the specific halogen series gas can be removed when the same amount of the hydrogencarbonate is used.
Although the mechanism is not clearly understood, it is considered that the added specific acid gas accelerates decomposition of a hypohalogenous acid salt formed due to reaction of Cl2, Br2 or I2 with the hydrogencarbonate. Usually, when Cl2, Br2 or I2 reacts with a hydrogencarbonate, a hypohalogenous acid salt is formed in accordance with the formula 1. In a case where sodium hydrogencarbonate is employed as the hydrogencarbonate, the formed hypohalogenous acid salt is known to decompose into sodium halide and oxygen in accordance with the formula 2. However, it is considered that, in a case where the hypohalogenous acid salt does not undergo decomposition and remains, the reaction of the hydrogencarbonate with Cl2, Br2 or I2 is less likely to proceed and reach a state of equilibrium.
In the present invention, it is considered that by addition of the specific acid gas, the specific acid gas (such as HX) decomposes the hypohalogenous acid salt into a halide and a hypohalogenous acid in accordance with the formula 3, whereby the removal efficiency of the specific halogen series gas increases. Here, the hypohalogenous acid is known to quickly decompose into hydrogen halide and oxygen in accordance with the formula 4.
NaHCO3+X2xe2x86x92NaXO+CO2+HXxe2x80x83xe2x80x83Formula 1 
(X=Cl, Br or I)
NaXOxe2x86x92NaX+1/2O2xe2x80x83xe2x80x83Formula 2 
NaXO+HXxe2x86x92NaX+HXOxe2x80x83xe2x80x83Formula 3 
HXOxe2x86x92HX+1/2O2xe2x80x83xe2x80x83Formula 4 
In the present invention, it is also preferred to pack the granulated product of a hydrogencarbonate in a container such as a packed tower together with activated carbon and to bring the present halogen gas-containing gas having the specific acid gas added thereto into contact therewith to remove the present halogen gas. By this method, not only the removal amount of the present halogen gas can be increased, but also generation of odor from activated carbon can be decreased as compared with a case where activated carbon alone is used. Specifically, a method of disposing the granulated product of a hydrogencarbonate and activated carbon in a layer structure as packed beds in a container such as a packed tower may be mentioned.
(2) Installation of a Catalyst Layer
In the present invention, it is preferred to pack a catalyst containing at least one element selected from the group consisting of Pd, Fe, Ni, Co, Mn and Cu (hereinafter referred to as specific metal element) in a hollow cylindrical container (column) to form a catalyst layer, to pack the granulated product of a hydrogencarbonate adjacent to the catalyst layer to form a granulated product layer, and to make the specific halogen series gas flow through the catalyst layer first and then flow through the granulated product layer. A space or a perforated plate as a partition panel may be provided between the catalyst layer and the granulated product layer. The catalyst layer can be used repeatedly, whereas the capacity to treat the specific halogen series gas of the granulated product layer disappears in a relatively short period of time as compared with the catalyst layer, and accordingly it may be favorable to provide a space or a partition panel when the exhaust granulated product is renewed in some cases. However, from a practical viewpoint, there is no problem to form the granulated product layer to be in contact with the catalyst layer without providing such a space or a partition panel. In the present invention, the catalyst layer is effective for increasing reactivity of the granulated product layer to increase utilization efficiency of the granulated product layer, and from such a viewpoint, it is also preferred that the catalyst layer and the granulated product layer are in contact with each other.
As the catalyst containing the specific metal element, preferred is a catalyst having the specific metal element supported by a carrier (such as activated carbon, zeolite or silica gel). The specific metal element in the catalyst is present preferably in a state of a metal element but it may be present in a state of a metal compound or in a state of a mixture of a metal element with a metal compound.
The content of the specific metal element in the catalyst layer is preferably from 0.0001 to 10% (proportion of the mass of the total specific metal elements as calculated as metal elements based on the total catalyst mass). If the content is less than 0.0001%, no adequate effect to improve reactivity of the granulated product layer can be obtained, and if the content exceeds 10%, no further improvement in reactivity of the granulated product layer tends to be obtained, and an unnecessary amount of the specific metal element may be used. The content is particularly preferably from 0.1 to 2%.
The catalyst containing the specific metal element is preferably porous, but a non-porous catalyst may be used. The shape of the catalyst may be any of aggregates, needles and flakes. The mean particle diameter of the specific metal element component in the catalyst is preferably at most 0.1 xcexcm so as to enlarge the specific surface area to increase the catalytic activity.
In the present invention, it is also preferred to further bring the specific halogen series gas into contact with an activated carbon layer in addition to the catalyst layer and the granulated product layer. In such a case also, the granulated product layer is located downstream the catalyst layer, however, the activated carbon layer may be located upstream the catalyst layer, between the catalyst layer and the granulated product layer, or downstream the granulated product layer. By disposing the activated carbon layer in addition to the catalyst layer and the granulated product layer and bringing the specific halogen series gas into contact therewith, load of the activated carbon layer can remarkably be reduced as compared with a case where a halogen element and a halogen compound are removed from the specific halogen series gas by the activated carbon layer alone, and generation of odor from the activated carbon layer can also be reduced.
(3) Addition of a Substance Containing the Specific Metal Element to the Granulated Product
In the present invention, it is also preferred to mix a substance containing the specific metal element (hereinafter referred to as the specific metal-containing substance) to a powder of a hydrogencarbonate having a mean particle diameter of primary particles of from 10 to 500 xcexcm, followed by granulation, and to bring the specific halogen series gas into contact with the obtained granulated product to remove the specific halogen series gas. The metal-containing substance may be a metal element, a metal compound or a mixture thereof.
By inclusion of the specific metal-containing substance in the granulated product, reactivity of the hydrogencarbonate can be improved, and the effect can be maintained for a long period of time. As a method of inclusion of the specific metal-containing substance into the granulated product, preferred is a method of mixing the specific metal-containing substance with the hydrogencarbonate, followed by granulation, The content of the specific metal-containing substance in the granulated product is preferably from 0.001 to 10 mass %. If the content is less than 0.001 mass %, no effect to improve the reactivity of the granulated product tends to be obtained, and if it exceeds 10 mass %, no further improvement in reactivity tends to be obtained, and an unnecessary amount of the specific metal-containing substance may be used, and further, the content of the hydrogencarbonate decreases, whereby the capacity to remove the halogen series gas tends to decrease. The content is particularly preferably from 0.005 to 5 mass %. As another material which may be contained in the granulated product, an adsorbent other than a hydrogencarbonate or a binder may, for example, be mentioned.
In the granulated product, in the same manner as mentioned above, the hydrogencarbonate reacts with a halogen element or a halogen compound to form a water-soluble salt, and the hydrogencarbonate itself is water-soluble, and accordingly most of the granulated product except for the specific metal-containing substance can be dissolved in water after used to remove the halogen series gas in an exhaust gas. The specific metal-containing substance can be recovered by filtration after the granulated product is dissolved in water.
By adding the specific metal-containing substance in the granulated product, the reactivity of the hydrogencarbonate with a halogen improves, and a larger amount of the halogen series gas can be removed when the same amount of the hydrogencarbonate is used. The mechanism also is not clearly understood similarly to the above-mentioned method of introducing the specific acid gas, but it is considered that the substance containing the above element accelerates decomposition of a hypohalogenous acid salt to be formed when the hydrogencarbonate reacts with Cl2, Br2 or I2 contained in the halogen series gas. It is considered that by mixing a metal or a metal compound in the granulated product, a decomposition reaction of the hypohalogenous acid salt is accelerated, and the removal efficiency of the specific halogen series gas increases.
Now, the present invention will be described in further detail with reference to Examples and Comparative Examples. However, it should be understood that the present invention is by no means restricted to such specific Examples.
In each of the following Examples, the hardness (breaking strength) of the granulated product was measured by using Kiya Type Digital Hardness Meter KHT-20 Model, manufactured by Fujiwara Scientific Co., Ltd. Further, since the hardness differs depending upon the size of the particles, measurement was carried out with respect to particles having uniform particle diameters obtained by sieving.
The mean particle diameter was measured as follows. Standard sieves (inner diameter: 200 mm, wire mesh: stainless steel) having sieve openings of 3.35 mm, 2.80 mm, 2.36 mm, 2.00 mm, 1.70 mm and 1.00 mm, respectively, were overlaid on top of one another, a bottom tray was disposed at the basement, and 100 g of a granulated product of a powder of a hydrogencarbonate was sprinkled on the top thereof, followed by shaking by a Ro-Tap Sieve Shaker (290 horizontal revolutions and 165 Taps per minute motion) manufactured by Iida Seisakusho for 10 minutes. Then, a mass of oversize particles remaining on each standard sieve was measured, a cumulative mass of the oversize particles remaining on each of sieves having the respective sieve opening values was shown by a line graph, and the particle diameter when the cumulative mass of the oversize particles was 50% was taken as the mean particle diameter.